This invention relates to a thin layer depositing apparatus capable of regulating gas pressure profile of a reaction gas to bring it in a desired condition.
To deposit thin layers such as conductive films, insulating films, etc. during the manufacture of various parts of electronic devices, there have been adopted thin layer depositing apparatuses. Among these, sputtering apparatuses have recently widely been used in order to improve adherence, grain size, and flattening of films covering the unevenness of the surface of a substrate.
On depositing thin layers using such sputtering apparatuses, the gas pressure profile of reactive gas introduced in a reaction vessel substantially affects the quality of the deposited layer. The gas pressure profile becomes best when the reactive gas is so introduced within the reaction vessel that the diffusion speed along the reactive gas flow is equal to or faster than the diffusion speed to the horizontal direction of the gas flow.
FIG. 1 shows a skeleton diagram illustrating a conventional sputtering apparatus wherein the reference numeral 1 designates a reaction vessel and 2 denotes a reactive gas inlet. The numeral 3 refers to a reactive gas outlet positioned sufficiently away form the inlet 2. Reactive gas is introduced in the reaction vessel 1 from the inlet 2 as shown by the arrow mark. The introduced reactive gas expands and diffuses as advancing in, so that the gas pressure at point A is considerably higher than that at point B.
Accordingly, the relation between the longitudinal diffusion speed V.sub.x and the O transverse diffusion speed V.sub.y is considered to be expressed by V.sub.x .gtoreq.V.sub.y. Considering, however, that the thermal motion velocity v of the reactive gas (.perspectiveto..sqroot.kT/m) (T=temperature, m=molecular weight and K=constant) and the horizontal diffusion speed V.sub.y are substantially the same, it is difficult to satisfy the above-mentioned relation V.sub.x .gtoreq.V.sub.y. The reactive gas also diffuses to the directions as shown by the dotted lined arrows, resulting in expansion about the reactive gas inlet 2, and the desired gas pressure profile cannot easily be obtained. In order to satisfy the relation V.sub.x .gtoreq.V.sub.y, there is proposed herein a method to increase the amount of the gas to be introduced, namely to form the entire body of the reaction vessel as a nozzle and to rapidly discharge the reactive gas, using a vacuum pump with large capacity, so as to rectify the gas flow to the longitudinal direction (x direction) as shown in FIG. 2(A) and increase the gas speed V.sub.x as it gets nearer to the outlet 3. To realize the proposal, however, not only a powerful discharge apparatus is necessary, but also the amount of the reactive gas to be used increases. Therefore the cost increases, and it is difficult to properly regulate the reactive gas, resulting in difficulty in obtaining the desired gas pressure profile.
Such impossibility of obtaining the desired gas pressure profile causes scattering of sputtering material as well as diminution of kinetic energy due to reduction of mean free path, and insufficiency of sputtering rate or abnormal growth of the layer due to re-adhesion of the scattered sputtering material on the target.
Particularly when it is desired to obtain a thin layer with good crystallization i.e. when obtaining a thin layer simultaneously satisfying the c axis orientation and theoretical chemical composition of the layer, we could only select the medium point of each of the above-cited conditions as the best condition for satisfying both of them, because those requirements have opposite dependencies on the gas pressure profile, respectively. Those problems have been evident in case of depositing a layer of conjugated material such as oxides and nitrides. A solution has been long needed for this.